Recently, hybrid vehicles have received great attention against the background of environmental issues. A hybrid vehicle is a vehicle on which a plurality of motive power sources are mounted, and a hybrid vehicle using an electricity storage device (battery, capacitor or the like) and a motor, in addition to a conventional engine, as motive power sources has already been put into practice.
Furthermore, a fuel cell vehicle on which a fuel cell is mounted as a motive power source also receives attention. A vehicle equipped with an electricity storage device such as a battery or a capacitor, in addition to a fuel cell, as an electric power supply is also a hybrid vehicle equipped with a plurality of motive power sources, in a broad sense.
On the other hand, a hybrid vehicle with an external charging function of charging an electricity storage device using an external electric power supply is known. According to the hybrid vehicle with an external charging function, if the electricity storage device can be charged, for example, by a commercial power supply at home, advantageously, the frequency of going to refueling stations for fuel fill can be reduced.
Japanese Patent Laying-Open No. 8-154307 discloses a hybrid vehicle including a charging function from the outside of the vehicle to an electricity storage device. This hybrid vehicle includes a battery which can be charged by an external charger, an electric motor driving wheels by electricity from the battery, control means for controlling an operation of the electric motor, an internal combustion engine used directly or indirectly for driving wheels, and travel time relation amount calculation means for calculating the amount related with a travel time since charging of the battery by the external charger. Then, the control means restricts an output of the electric motor when a travel time relation amount calculated by the travel time relation amount calculating means reaches a prescribed amount.
In this hybrid vehicle, the output of the electric motor is restricted when the vehicle travels for a long time without external charging, and the output of the electric motor is inevitably restricted when the vehicle continues to travel while using the fuel by the internal combustion engine. Accordingly, the driver is prompted to carry out external charging. Therefore, according to this hybrid vehicle, the dependency on the internal combustion engine can be reduced.
The hybrid vehicle disclosed in Japanese Patent Laying-Open No. 8-154307 as described above restricts the operation of the internal combustion engine. Furthermore, in other hybrid vehicles, it is expected that, in the future, with increased capacity of the electricity storage device and even with provision of the external charging function, the electric vehicle mode (EV mode) of traveling only with electricity from the electricity storage device will be mainly used and the operation frequency of other motive power sources (internal combustion engine, fuel cell, and the like) will be reduced.
However, in the motive power sources with less operation frequency, it is likely that good conditions cannot be kept and that discovery of abnormalities is delayed. For example, if a non-operating state of an internal combustion engine continues for a long term, the condition of the internal combustion engine is deteriorated, and moreover, the delayed discovery of abnormalities may lead to a serious failure.
Moreover, if the EV mode is mainly used, the users' desire to enjoy riding by driving other motive power sources (for example, riding by driving the internal combustion engine) may arise.